A polymer electrolyte membrane fuel cell (PEMFC) system typically includes a stack, a reformer, a fuel tank, and a fuel pump. The polymer electrolyte membrane fuel cell system supplies fuel in the fuel tank to the reformer by operating the fuel pump, generates hydrogen gas by reforming the fuel in the reformer, and generates electric energy by electrochemically reacting hydrogen with oxygen.
A direct methanol fuel cell (DMFC) is capable of directly supplying a liquid methanol fuel to the stack. A direct methanol fuel cell system is more advantageous in view of miniaturization because it does not use the reformer, unlike the polymer electrolyte membrane fuel cell system discussed above.
The stack of a fuel cell has a structure that several to several tens of unit cells, which are typically composed of a membrane electrode assembly (MEA) and a separator, are stacked. The membrane electrode assembly has a structure to which an anode electrode (namely, “fuel electrode” or “oxidation electrode”) and a cathode electrode (namely, “air electrode” or “reduction electrode”) are attached, with the polymer electrolyte membrane therebetween. The stack of the fuel cell is compressed and sealed to prevent non-uniform operating conditions such as pressure drop or oxygen decrease inside the stack.
An air pump can be mounted on the PEMFC or DMFC fuel cell system in order to supply an amount of oxygen necessary for obtaining a desired energy output to the fuel cell.
However, in the transportable fuel cell system used as a mobile power source or a transportable power source, a serious operational problem of the fuel cell may occur due to various contaminants in the air being taken into the fuel cell, according to changes in the location its use. The fuel cell is operated depending on the elaborately equilibration-controlled chemical reaction, which may be adversely affected by the contaminants in the air. Possible contaminants in the air include, for example, small particles floating in air such as dust, smog and smoke particles, etc.; hydrocarbon-based substances such as aromatic hydrocarbon, methanol, butane and propane; and volatile organic compounds such as ammonia, ozone, hydrogen sulfide, sulfur oxide, nitrogen compound and carbon monoxide, etc. Therefore, in most transportable fuel cell systems, a filtering system suitable for removing various contaminants in air has been required.
In the transportable fuel cell system, it is generally necessary to reduce the weight and the volume of the air supply system so that transportation and portability of the fuel cell system, on which the air supply system including the air pump and the filtering system is mounted, can be easy. Therefore, in the conventional transportable fuel cell system, there is a need of an air supply system suitable for miniaturization.
The air pump to be mounted on the transportable fuel cell system supplies air to the fuel cell through an air movement device such as a fan or a compressor positioned in an airflow stream. However, the air pump unfortunately generates a considerable level of noise. Herein, “noise” means unpleasant sound waves generated from moving parts, such as a rotor, an impeller, a vane, or a piston of the air pump. Therefore, in order to use the fuel cell system as a power source of a portable communication terminal, etc., such as a low noise notebook computer, it is necessary to reduce the noise of the air pump in the fuel cell system below proper levels.